1. Field of the Invention
The invention relates to a reflector discharge lamp in which a discharge lamp is combined with a concave reflector. The invention relates especially to a reflector discharge lamp in which a mercury lamp of the short arc type or metal halide lamp likewise of the short arc type is used as the discharge lamp, and which is used for a liquid crystal projector or the like.
2. Description of the Related Art
Recently liquid crystal projectors have been drawing attention. As their light source device, a reflector discharge lamp is used in which a discharge lamp of the short arc type is installed in a concave reflector.
There is a need to reduce the size of metal halide lamps which are used for liquid crystal projectors and the like. Therefore, a small lamp with a total lamp length of 65 mm is used. This lamp is installed in a reflector and is used to increase light efficiency.
Furthermore, recently there has generally been a front cover on the front side of the reflector to prevent, in the unwanted case of breakage of the lamp during operation, the high temperature fragments formed thereby from being flung into the surroundings.
This technology is disclosed, for example, in Japanese patent disclosure document HEI 5-251054 and Japanese patent disclosure document HEI 6-203806.
In a reflector discharge lamp in which the front of the reflector is covered with a front cover, however, the space in the reflector is essentially in a sealed state. Therefore, during operation, the lamp reaches an extremely high temperature. With regard to the fact that, in the emission space emission metals which fill it should vaporize well, it can also be imagined that a certain temperature increase is desirable. However, in the hermetically sealed portions with a foil seal arrangement, such defects as breaking of the foil and the like occur due to oxidation that results due to high temperature.